From CNN/Money:

In a clear sign that the credit crunch is still affecting the nation's largest financial institutions, the Federal Reserve agreed this week to bend key banking regulations to help out Citigroup and Bank of America.

The regulations in question effectively limit a bank's funding exposure to an affiliate to 10% of the bank's capital. But the Fed has allowed Citibank and Bank of America to blow through that level. Citigroup and Bank of America are able to lend up to $25 billion apiece under this exemption, according to the Fed. If Citibank used the full amount, "that represents about 30% of Citibank's total regulatory capital, which is no small exemption," says Charlie Peabody, banks analyst at Portales Partners.

So, how serious is this rule-bending? Very. One of the central tenets of banking regulation is that banks with federally insured deposits should never be over-exposed to brokerage subsidiaries; indeed, for decades financial institutions were legally required to keep the two units completely separate. This move by the Fed eats away at the principle.